Pythonand Zope

An IntroductionKiran Jonnalagadda<jace@seacrow.com>

http://jace.seacrow.com/

What kind of a language is Python?

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High Level & Low Level

Low level languages give you more power, but take very long to write code in.

High level languages emphasise developer productivity; get things done fast.

High Level

Lisp

Perl

Python

Java, C#

C++

C

Assembler

Low Level

Powe

r — P

rodu

ctiv

ity

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Why Productivity?

Computers get faster each year.

Humans don’t get faster.

Language that can make programmer faster makes sense.

Drop in program’s speed is offset by a faster computer.

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Types of Languages

How does the language treat variables?

Type is Strong or Weak

Declaration is Static or Dynamic

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Strong Typed

Type of variable is explicit.

Type of variable does not change depending on usage.

Examples:In C++, Java or C#: int n;n = 0; // validn = 0.6; // invalid

In Python: a = 1b = “hello”print a + b # invalid

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Weak Typed

Type of variable is NOT explicit.

Type of variable depends on the operation.

Examples:In shell script (bash): A=1B=2echo $A+$B # 1+2echo $((A+B)) # 3

In PHP: $a = 1;$b = 2;echo($a + $b); # 3echo($a . $b); # 12

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Static Typed

Variable is declared before use.

Using a variable without declaring it is a compile-time error.

Type of variable cannot be changed at run-time.

Examples:In C, C++, Java, C#: int n;n = 1; // validm = 1; // invalid

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Dynamic TypedVariables need not be declared before use.

However, variables do not exist until assigned a value.

Reading a non-existent variable is a run-time error (varies by language).

Examples:In shell script (bash):A=1echo $A # 1echo $B # (blank)

In Python: a = 1print a # 1print b # (error)

Language Type Matrix

Static Typed Dynamic Typed

Weak Typed C Perl, PHP,Shell Script

Strong Typed C++, Java, C# Python

Capability MatrixOS Level GUI Web Portable

Perl Yes Yes Yes

Python Yes Yes Yes

Java, C# Yes Yes Yes

VB Yes Yes

PHP Yes Yes

C++ Yes Yes Yes Yes

C Yes Yes Yes Yes

Features MatrixOO GC Introspection ADT*

Perl Partial Yes Partial Yes

Python Yes Yes Yes Yes

Java, C# Yes Yes Partial Yes

VB Partial Yes Partial

PHP Partial Yes Partial

C++ Partial

C* Advanced Data Types: strings, lists, dictionaries, complex numbers, etc.

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What is Introspection?

Concept introduced by Lisp.

Code can treat code as data.

Can rewrite parts of itself at run-time.

Very powerful if used well.

Python takes it to the extreme.

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Highlights of Python

No compile or link steps.

No type declarations.

Object oriented.

High-level data types and operations.

Automatic memory management.

Highly scalable.

Interactive interpreter.

Python is all about

Rapid Application Development

Example CodeUsing the Python Interactive Interpreter: >>> myStr = "Rapid Coils">>> myStr.split(" ")[0][:-2].lower() * 3'rapraprap'

>>> myLst = [1, 2, 3, 4]>>> myLst.append(5)>>> "|".join([str(x) for x in myLst])'1|2|3|4|5'>>>

Example CodeDictionaries or hash tables or associative arrays: >>> myDict = {1:['a','b','c'],2:"abc"}>>> myDict[3] = ('a','b','c')>>> myDict.keys()[1, 2, 3]>>> myDict['foobar'] = 'barfoo'>>> myDict.keys()[1, 2, 3, 'foobar']>>> myDict{1: ['a', 'b', 'c'], 2: 'abc', 3: ('a', 'b', 'c'), 'foobar': 'barfoo'}>>>

Python ClassesClasses are defined using the “class” keyword: >>> class foo:... def __init__(self, text):... self.data = text... def read(self):... return self.data.upper()... >>> f = foo("Some text")>>> f.data'Some text'>>> f.read()'SOME TEXT'>>>

InheritanceClasses can derive from other classes: class Pretty: def prettyPrint(self, data): print data.title().strip()

class Names(Pretty): def __init__(self, value): self.name = value def cleanName(self): self.prettyPrint(self.name)

Multiple inheritance is allowed.

Operator Overloadingclass Complex: def __init__ (self, part1, part2): self.real = part1 self.im = part2

def __add__ (self, other): return Complex(self.real + other.real, self.im + other.im)

>>> a = Complex(1, 2)>>> b = Complex(2, 3)>>> c = a + b>>> print c.real, c.im3 5>>>

Container Model>>> class foo:... pass... >>> class bar:... pass... >>> f = foo()>>> b = bar()>>> dir(f)['__doc__', '__module__']>>> f.boo = b >>> dir(f)['__doc__', '__module__', 'boo']

Observe how items are added to containers.

So that is Python. What is Zope?

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Zope is...An application built using Python.

Provides a Web server,

A database engine,

A search engine,

A page template language,

Another page template language,

And several standard modules.

What Visual Studio is to

Windows software development,

Zope is to the Web.

Zope is a Web Application Server.A framework for building applications with Web-based interfaces. Zope provides both development and run-

time environments.

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Web Server: ZServer

Uses ZServer; Apache not needed.

But Apache can be used in front.

ZPublisher maps URLs to objects.

ZServer does multiple protocols:

HTTP, WebDAV and XML-RPC.

FTP and Secure FTP (SFTP in CVS).

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Database Engine: ZODB

Zope Object Database.

Object oriented database.

Can be used independent of Zope.

Fully transparent object persistence.

May be used for either relational or hierarchical databases, but Zope forces hierarchical with single-parent.

Hierarchical Data Access

Python:Object.SubObj.Function()

ZServer URL:site.com/Object/SubObj/Function

The only way to get to “Function” is via “Object” and “SubObj.”

Introducing Acquisition...

Object

SubObj

Function

How Acquisition Works

Container.SubObj.SubSubObj.Template is the same thing as Container.Template, but context differs.

Container

Template

SubObj

SubSubObj

What Inheritance is to

Classes,

Acquisition is to Instances

and Containers.

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ZODB FeaturesCode need not be database aware.

Includes transactions, unlimited undo.

Storage backend is plug-in driven.

Default: FileStorage.

Others: Directory and BerkeleyDB.

May also be an SQL backend.

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ZODB with ZEOZEO is Zope Enterprise Objects.

One ZODB with multiple Zopes.

Processor usage is usually in logic and presentation, not database.

ZEO allows load to be distributed across multiple servers.

Database replication itself is not open source currently.

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Search Engine: ZCatalog

ZCatalog maintains an index of objects in database.

Is highly configurable.

Multiple ZCatalog instances can be used together.

No query language; just function calls.

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Document Template ML

DTML uses <dtml-command> tags inserted into HTML.

Common commands: var, if, with, in.

Extensions can add new commands.

DTML is deprecated: difficult to edit with WYSIWYG editors.

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Zope Page Templates

ZPT uses XML namespaces.

Is compatible with WYSIWYG editors like DreamWeaver.

Enforces separation between logic and presentation: no code in templates.

Example:<span tal:replace="here/title”>Title comes here</span>

Zope Page TemplatesBoxSlot

Main BodySlot

Templates define macros and slots using XML namespaces. Macros fill slots in other templates.

File-system Layout Zope/ The base folder doc/ Documentation Extensions/ Individual Python scripts import/ For importing objects lib/ Libraries python/ Zope’s extensions to Python Products/ Extensions to Zope var/ Data folder Data.fs The database file ZServer/ Web server

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Example Extension: Formulator

HTML form construction framework.

Form widgets ⇔ Formulator objects.

Widgets can have validation rules.

Automatic form construction.

Or plugged into a ZPT template.

Painless data validation.

Supported Platforms

Windows Linux FreeBSD Mac OS XSolaris

Red Hat Debian Mandrake SuSE Gentoo

OpenBSD

Supported Operating Systems

Supported Linux Distributions

Resources

Python: www.python.orgZope: www.zope.org

The Indian Zope and Python User’s Groupgroups.yahoo.com/group/izpug